1. Field of the Invention
The invention relates to semiconductor wafer processing. Specifically the invention relates to a method for the precise singulation of integrated circuit die from a semiconductor substrate.
2. Description of the Prior Art
Semiconductor processing generally comprises multiple photolithographic, etching, plating and doping steps to form an array of individual integrated circuit die on the surface of a semiconductor substrate such as a wafer. Integrated circuit die densities frequently range in the thousands of die per wafer, each die of which is separated from the others by a narrow inactive boundary referred to as a die “street”. Once integrated circuit die fabrication and test at the wafer level is complete, the individual die are “singulated” from the wafer for subsequent leadframe attachment, wirebonding and encapsulation. Singulation is typically accomplished by cutting along the die streets using a dicing saw.
Automated dicing saws use specialty dicing blades commonly ranging from 1-10 mils in width, which singulate the individual die from the wafer by cutting along the die streets. This mechanical method of singulation retains the undesirable attributes of backside wafer chipping and the characteristic “kerf” along the saw cut, which is the width of the blade plus an additional width associated with mechanical tolerances of the saw and blade. For instance, a dicing blade that is 35 microns in width may have a 40-42 micron kerf width, dependent on saw set up.
Applications where very high tolerance die singulation is required cannot accommodate the tolerances associated with blade dicing or, for that matter, laser dicing. One such application relates to focal plane array integrated circuit chips used in four-sided, buttable stacks of interconnected die for use in large area mosaic focal plane detector arrays. In such applications, die edge tolerances must be one micron or less to minimize loss of optical information and to maintain the buttability of the stacks. The requirement of providing half-pixel or less separation between detector stacks can be met by defining the edge of a detector die using an optically precise, photolithographic-based dicing technique. Large arrays can be assembled from these stacks to form curved (concave or convex) mosaic focal plane arrays.
Precision die singulation applications have requirements for detector die to be diced within one micron of active features on the die. Standard precision dicing is on the order of ±3 microns and cannot meet the high tolerances noted above. Further, the edges of the detectors are required to be highly orthogonal to each other to ensure accurate buttability. Existing dicing means do not provide the necessary accuracy for the above applications.
What is needed is a method for precision die singulation method which overcomes these limitations in the prior art.